In advancement of digital technologies of electronic devices, there has been an increasing demand for a larger capacity of a nonvolatile resistance variable element, reduction of a write electric power in the element, reduction of write/read time in the element, and a longer life of the element to store data of images and so on. It is said that in response to such a demand, there is a limitation in miniaturization of a FLASH memory using the existing floating gate.
As a first prior art which possibly meets such a demand, there has been proposed a nonvolatile resistance variable element using perovskite materials (e.g., Pr(1-x)CaXMnO3 [PCMO], LaSrMnO3 [LSMO], GdBaCoXOY [GBCO] or the like) (see Patent document 1). This technique is such that the perovskite material is applied with predetermined voltage pulses (wave-shaped voltages which are short in duration) which are different in polarity (or are the same in polarity and different in voltage values) to increase or decrease its resistance value and the changed resistance value is caused to correspond to data, thereby storing data.
As a second prior art, there is a nonvolatile resistance variable element making the use of an event that a resistance value of a layer of a transition metal oxide (NiO, V2O, ZnO, Nb2O5, TiO2, WO3, or CoO) is changed by applying the above mentioned voltage pulses to the transition metal oxide layer (see Patent document 2).
As a third prior art, there is a nonvolatile resistance variable element in which an amorphous oxide (e.g., oxide of one or more elements selected from Ti, V, Fe, Co, Y, Zr, Nb, Mo, Hf, Ta, W, Ge, and Si) is provided with Ag or Cu electrode and is applied with a voltage to allow the electrode material Ag or Cu to be ionized and diffuse into a thin layer, thereby changing the resistance value of the amorphous oxide (see patent document 3).
As a fourth prior art, there is proposed a resistance variable element which includes a material layer having a spinel structure which is sandwiched between electrodes and is configured to change to a high-resistance state and a low-resistance state in response to electric pulses which are different in polarity (bipolar-driven) (Patent documents 4 and 5).
By using the above mentioned resistance variable materials as memory cells and combining them with transistors for selecting respective memory cells, the operation of the nonvolatile resistance variable element is attained.    Patent document 1: U.S. Pat. No. 6,204,139    Patent document 2: Japanese Laid-Open Patent Application Publication No. 2004-363604    Patent document 3: Japanese Laid-Open Patent Application Publication No. 2004-342843    Patent document 4: Japanese Laid-Open Patent Application Publication No. 2005-317787    Patent document 5: Japanese Laid-Open Patent Application Publication No. 2006-080259